1. Field of the Invention
The present invention relates to an electromagnetic actuator and, in particular, especially to an electromagnetic actuator which can drive a driven member while detecting a position of the driven member.
2. Description of Related Art
An electromagnetic actuator which drives a driven member has needed a position sensor for detecting an actual position of the driven member which sensor is separate from the electromagnetic actuator itself. To solve this problem, as well as to make the costs lower and to save space, the applicant proposed such an electromagnetic actuator which involves a movable member as a driven member being driven while detecting the actual position of the movable member in Japanese Patent Kokai 8-275460. The outline of this apparatus is as shown in FIG. 1. In FIG. 1, an electromagnetic coil 3 is wound around a yoke 5. A pair of magnetic poles 101 and 102 of the yoke 5 are located to face each other via an air gap to distribute a magnetic flux thereby to form a magnetic field therebetween. Within the magnetic field between the magnetic poles 101 and 102, there is disposed a rotor 6 made of magnetic component 103 provided with a pair of permanent magnets 10 and 11. Moreover, a Hall sensor 8 which detects the magnetic flux density is provided in the proximity area between magnetic poles 101 and 102. It is now apparent that this apparatus is an electromagnetic actuator which rotates the rotor 6 up to a desired angular position by the varying strength of a magnetic field established by a magnetic flux formed inside the yoke 5, the magnetic flux being formed by supplying a source current to the electromagnetic coil 3.
However, this type of electromagnetic actuator has such an inconvenience that the detection sensitivity of this type remains low because the Hall sensor 8 detecting the rotation angle of rotor 6 is located in the magnetic field formed by the magnetic flux distributed by the magnetic coil 3, and the density of magnetic flux passing through the Hall sensor is low. Moreover, there is another inconvenience that, freedom in design of a driving mechanism in the electromagnetic actuator is restricted in order to spare some space for a Hall sensor to be provided. Furthermore, there even happened that a Hall sensor could not be installed with the driving mechanism because of restrictions in structure of driving mechanism.
When, moreover, there adopted such a design that the voltage signal emitted from a Hall sensor is processed after detecting the sample value by a sampling circuit, that is, for example, a voltage signal is incorporated through the analog-digital conversion circuit and is processed based on the obtained sample value, a voltage transformation circuit is needed to transform the voltage signal received from a Hall sensor into a voltage signal having a voltage level appropriate to the input range of the sampling circuit. If the circuit is so composed as mentioned above, the amplification rate of the voltage transformation circuit is to be adjusted in accordance with the sensitivity of the Hall sensor or the dispersion of the resistance values of circuit components, thereby causing the costs to rise up or needing an improved accuracy in the adjustment.
The present invention has been made to solve such problems mentioned above and to provide an electromagnetic actuator which can detect precisely the location of the driven member by detecting the density of magnetic flux where the density is high. The driving mechanism does not need the design change thereof. The position sensor is applicable for different structures of the driving mechanism. The actuator can detect precisely the position of the driven member by obtaining a voltage value of the voltage signal emitted from the Hall sensor with an appropriate resolution while being easily adjusted.
According to the present invention, an electromagnetic actuator comprises: a magnetic path component which is composed of a magnetic flux formation section provided with an electromagnetic coil and of a magnetic field formation part which causes a magnetic flux to form a magnetic field; a movable member which is disposed within said magnetic field and has magnetized surfaces differently magnetized from each other being movable in accordance with changes of said magnetic field, said magnetic field formation section having a plurality of magnetic poles corresponding to the magnetized surfaces of said movable member, so as to drive said movable member, and said magnetic path member having a magnetic gap at a magnetic path connecting said magnetic flux formation section with said magnetic pieces or within said magnetic flux formation section; magnetic flux density detecting means installed within said magnetic gap, for detecting said magnetic flux density distributed within said magnetic gap; detection means for detecting a magnitude of an electric current flowing through said electromagnetic coil; and calculating means for calculating the position of said movable member on the basis of the value of the magnetic flux density detected by said magnetic flux density detection means and on the magnitude of the current detected by said current detection means.
An electromagnetic actuator according to the present invention can precisely detect the position of a driven member since the magnetic flux density is detected at the magnetic gap provided within the magnetic flux forming means. Furthermore, with this arrangement it makes needless to change the design of the driving mechanism and enables this magnetic flux density detecting means to use together with different structure of a driving mechanism.